It is known in the art to form a surfactant system using a petroleum sulfonate, brine, and a cosurfactant, such as an alcohol. It is known that the cosurfactant should be a material having moderate solubility in water and excellent surfactant systems can be made using a cosurfactant with a solubility in water within the range of 0.5 to 20 grams per 100 grams of water. However, a cosurfactant having what would otherwise appear to be ideal solubility characteristics, may in fact not be optimum for a given type of oil.